The invention relates to a process and a device for the manufacture of hollow plastic bodies, particularly of plastic bottles.
In the production of hollow plastic bodies, such as PET bottles, for example, so-called xe2x80x98plastic molding blanksxe2x80x99 (pre-forms), which are brought to their definitive shape during the course of the process, are used. Such types of plastic molding blanks are generally cylindrical hollow bodies which are closed at one end, and which are formed by means of injection molding, for example. These molding blanks are conveyed to a tempering station, in which they are heated to the temperature which is necessary for the following extension blowing process. During this extension blowing process, the hollow plastic body is then produced with its definitive shape.
A process of this type is described in the European patent document EP 0060 521, for example. In that document, the molding blanks are transported suspended on shuttle units along a guide rail with their apertures directed upwardly. The guide rail guides them through the tempering station and the blowing forming station.
During the manufacturing process, however, it may be desirable if the spatial orientation of the molding blanks can be changed. It can be advantageous if the molding blanks are oriented with their apertures directly downwardly, such as in the tempering station, for example.
A turning device in which the plastic molding blanks are transported in carrier units, which have a mechanism that makes a turning of the plastic molding blanks possible, is correspondingly described in the German patent document DE 31 09 267 C2. For this purpose, each carrier unit is provided with a toothed gear, the one component of which is moved by means of a link guide unit along the transport path in such a manner that the plastic molding blank is turned by means of the toothed gear on the second part of the toothed gear. Such a device therefore requires a corresponding toothed gear in every carrier unit, and can thus only be produced at a great expense.
Other known devices for the manufacture of the hollow plastic bodies have gripping devices which transfer the plastic molding blanks from one transport device to the next one, and thereby change their spatial orientation. This is also relatively expensive.
The task of the present invention is to describe a process and a device with the help of which it is possible, in a simple way and manner, to change the spatial orientation of the plastic molding blanks.
In the process in accordance with the invention, the plastic molding blanks are turned in their spatial orientation, by means of a shuttle system, through the twisting or curving of at least one guide rail along the transport path. The device in accordance with the invention additionally has at least one correspondingly twisted of curved guide rail.
With these characteristics, it is possible to change the spatial orientation of the plastic molding blanks in a simple manner. A twisting or curving of the guide rail makes a changing of the spatial orientation possible without the molding blanks having to leave the shuttle system. The changing of the orientation of the plastic molding blanks takes place rapidly and precisely, and without the stressing of the molding blanks. Expensive gripping mechanisms or the like are not required.
In accordance with one advantageous configuration, the at least one guide rail is twisted or curved in such a manner that the plastic molding blanks are, before being admitted into the tempering station, turned into an upside down position, that is to say, with their apertures directed downwardly, so that they are transported in the tempering station with their apertures directed downwardly. Immediately after the tempering station, the molding blanks can again be brought, in a second twisting- or curving area, into their original suspended position, with their apertures directed upwardly.
The molding blanks can be transferred directly from a conveying rail to the shuttle system. A transfer wheel with accommodation pockets can also be provided, however. Such a transfer wheel brings the plastic molding blanks to that distance which corresponds to that spacing distance which is defined by the individual slide units in the shuttle system.
After passing through the tempering station, the molding blanks can be conveyed directly from the shuttle system to the blowing wheel of the extension blowing station. The intake star unit, which then transfers them to the blowing wheel at a defined distance, could also be inserted here.
In another configuration, the molding blanks can also be guided by the shuttle system through the blowing station, so that no transfer to another means of transport is necessary at the intake into the blowing station.
Inside the extension blowing station, the plastic molding blanks must have a greater distance than they do in the tempering station, in order to create space for the definitive expansion of the individual hollow plastic bodies which comes about during the extension blowing process.
This can be achieved, in a simple manner, through the fact that the distance of the individual slide units of the shuttle system is increased after passing through the tempering station.
For the purpose of driving, the slide units of the shuttle system may have projections or tongue units with which a drive device can engage, for example. With the help of the driving device, the slide units can be moved along the guide rail by means of these tongue units. It can thereby be sufficient to provide one single stationary driving device which moves each slide unit that is passing by, through which the slide units which are positioned next to one another are moved further along in a downstream direction. It is also conceivable, however, to carry out the driving by means of friction wheels or friction straps which engage on the slide units, and move these further along by means of a friction engagement. A driving by means of gravity is also possible.
In order to achieve a uniform tempering of the plastic molding blanks within the tempering station, it is advantageous if these are rotated around their longitudinal axis. In the device in accordance with the invention, this can be achieved, in a simple manner, through the fact that the slide units have holding devices for the plastic molding blanks which are supported in a rotatable manner, and which can be rotated around an axis which is directed perpendicularly to the direction of forward movement. A rotation around this axis can be brought about, in a simple manner, through the engagement of a stationary projection with the driving tongue units of the individual slide units. A rotational driving by means of friction would, however, likewise be possible.
One implementation of the machine as a whole which is particularly economical in terms of space is provided if the tempering station and the extension blowing station are, in the manner as known per se, positioned above one another, and thus at different levels. The change in the spatial levels which is thereby necessary can easily be achieved by means of a corresponding curved course of the guide rail immediately following the tempering station.
The molding blanks can be held on the slide units, such as by means of clamping elements, for example. It is particularly advantageous, however, if the molding blanks are held on the slide units with the help of a mandrel which engages with the aperture of the individual plastic molding blanks by means of a friction engagement.
The molding blanks can be applied to this mandrel with the help of an attaching mechanism.
One form of implementation provides that the distance of the mandrel from the guide rails can be altered against a spring force.
The mandrel can, in this manner, be first brought closer to the guide rail, such as by means of a corresponding link guide unit, for example, and, in order to accommodate a plastic molding blank, then be further removed from the guide rail, by means of a spring resistance, in order to engage with the aperture of the plastic molding blank.
One such configuration makes a rapid and precise assumption of the plastic molding blanks by the slide units possible.
The slide units can, however, also comprise detachable accommodation elements which are, together with the plastic molding blanks, transferred to the blowing wheel and are, after the extension blowing process, removed from the plastic molding blanks and connected to the slide units again.